XBAR Busbar Gap Dielectric Stripes to Suppress Gap Mode Spurs

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Solution Overview

Problem

Existing transversely-excited film bulk acoustic resonators (XBARs) suffer from acoustic energy leakage and undesired ripples in resonator admittance, leading to increased insertion loss due to gap mode spurs and energy leakage in the transverse direction.

Innovation Solution

Incorporation of gap dielectric stripes in busbar-electrode gaps to confine acoustic energy within the resonator area, reducing energy leakage and moving problematic gap mode spurs to less critical frequency locations, thereby improving device Q and reducing spur magnitude.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If traditional XBAR structure is used, then device simplicity is maintained, but acoustic energy leakage and insertion loss increase

Engineering Contradiction:

Improveacoustic energy leakageVSAvoiddevice structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent divides the continuous busbar electrode into segmented sections by introducing gap dielectric stripes between them. This segmentation creates acoustic confinement regions that prevent energy leakage while maintaining electrical connectivity through the dielectric-coupled gaps, directly resolving the contradiction between energy loss reduction and structural simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The gap dielectric stripes serve as intermediary elements positioned between busbar electrode sections. These dielectric structures mediate both acoustic confinement (blocking acoustic energy leakage) and electrical coupling (maintaining electrode connectivity), thereby reducing energy loss without significantly complicating the device architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If gap dielectric stripes are added for acoustic confinement, then acoustic energy leakage is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improveacoustic confinementVSAvoidfabrication process complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent combines multiple functions into the gap dielectric stripes: acoustic confinement, electrical insulation, and mechanical support. By merging these functions into a single structural element, the design achieves improved acoustic confinement while avoiding the need for separate components, thus limiting the increase in manufacturing complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The invention optimizes specific parameters of the gap dielectric stripes (width, thickness, material composition) to achieve effective acoustic confinement. By carefully controlling these parameters within manufacturable ranges, the patent achieves reliable acoustic confinement without requiring complex fabrication processes.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If busbar electrode gaps are left open, then fabrication is simpler, but acoustic energy leaks in transverse direction

Engineering Contradiction:

Improvetransverse energy leakageVSAvoidelectrode structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent converts the potentially harmful open gaps between busbar electrodes into beneficial acoustic confinement structures by filling them with dielectric material. The gaps that would normally allow acoustic energy leakage are transformed into acoustic barriers, turning a structural weakness into a performance advantage while maintaining electrical connectivity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The implementation of gap dielectric stripes enhances acoustic confinement, reduces device losses, and moves gap mode spurs to more favorable frequencies, improving the performance of XBAR filters, particularly in communications bands above 3 GHz.

Implementation Method 1

stripes of a dielectric material extending over ends of the interleaved fingers and portions of gaps between the ends of the interleaved fingers and opposing busbars of the IDT

Methodology Applied

Scientific EffectAcoustic confinement:

Implementation Method 2

an 82Y-cut lithium niobate piezoelectric plate attached to the surface of the substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12424999B2Transversely-excited film bulk acoustic resonators with gap dielectric stripes in busbar-electrode gaps

Publication Date: 2025.09.23 MURATA MFG CO LTD

AI summary

An acoustic resonator device includes a substrate having a surface; an 82Y-cut lithium niobate piezoelectric plate attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in an intermediate dielectric layer of the substrate; an interdigital transducer (IDT) at the piezoelectric plate such that interleaved fingers of the IDT are at the diaphragm; and a plurality of stripes of a dielectric material extending over ends of the interleaved fingers and portions of gaps between the ends of the interleaved fingers and opposing busbars of the IDT.